The present invention relates to phase shifters, interrogators, methods of shifting a phase angle of a signal, and methods of operating an interrogator.
Electronic identification devices, such as radio frequency identification devices (RFIDs), are known in the art. Such devices are typically used for inventory tracking. As large numbers of objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and flow of objects. Additionally, there is a continuing goal to determine the location of objects is in an inexpensive and streamlined manner. One way of tracking objects is with an electronic identification system.
One presently available electronic identification system utilizes a magnetic coupling system. In some cases, an identification device may be provided with a unique identification code in order to distinguish between a number of different devices. Typically, the devices are entirely passive (have no power supply), which results in a small and portable package. However, such identification systems are only capable of operation over a relatively short range, limited by the size of a magnetic field used to supply power to the devices and to communicate with the devices.
Another type of wireless electronic identification system is an active wireless electronic identification system. Attention is directed towards commonly assigned U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, now U.S. Pat. No. 6,130,602, which issued on Oct. 10, 2000, and incorporated herein by reference, which describes such active systems in detail. One such system is sold by Micron Communications Inc., 3176 S. Denver Way, Boise, Id. 83705 under the trademark Microstamp Engine ((trademark)).
These systems include integrated circuit devices which include an active transponder and are intended to be affixed to an object to be monitored. The devices are capable of receiving and processing instructions transmitted by an interrogator. A device receives the instruction, if within range, then processes the instruction and transmits a response, if appropriate. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter, circuit.
Because active devices have their own power sources, they do not need to be in close proximity to an interrogator or reader to receive power via magnetic coupling. Therefore, active transponder devices tend to be more suitable for applications requiring tracking of a tagged device that may not be in close proximity to an interrogator. For example, active transponder devices tend to be more suitable for inventory control or tracking.
The active transponder is capable of using backscatter communication techniques in responding to an interrogator. The interrogator outputs a polling signal followed by a continuous wave (CW) signal. The integrated circuit devices are configured to modulate the continuous wave signal in backscatter communication configurations. This modulation typically includes selective reflection of the continuous wave signal. The reflected continuous wave signal includes the reply message from the remote devices which is demodulated by the interrogator.
Certain drawbacks have been identified with the use of backscatter communication techniques. For example, the transmission of the continuous wave signal using the interrogator can desensitize the receiver of the interrogator during reception thereby of reply signals from associated remote devices. In particular, some of the continuous wave signal tends to bleed through to the received reply messages. Such results in degradation of wireless communications.
Systems have been provided which improve wireless communications without the drawbacks associated with conventional devices. Variable phase shifters can be used in such systems. However, conventional variable phase shifters are typically very expensive and typically only operate within a certain specified range, (e.g., 0 to 180 degrees).
The present invention includes variable phase shifters, interrogators, methods of shifting a phase angle of a signal, and methods of operating an interrogator.
It is desired to reduce power within a modulated return link continuous wave signal of a coherent backscatter communication system including an interrogator and at least one remote communication device. Exemplary remote communication devices include remote intelligent communication devices and radio frequency identification devices (RFID) of electronic identification systems.
An exemplary interrogator comprises a coherent interrogator configured to provide backscatter communications. More specifically, the interrogator is configured to output a forward link communication and a wireless continuous wave signal using a transmitter. The interrogator is also configured to output a local continuous wave signal to a receiver of the interrogator following transmission of the forward link communication. Provision of the local signal enables coherent operation of the interrogator. The interrogator is operable to receive return link communications from at least one remote communication device responsive to transmission of the forward link wireless communication.
The interrogator preferably includes a receiver operable to reduce the amplitude of a carrier signal of the return link communication. For backscatter communications, the remote communication device is configured to modulate the continuous wave signal providing a carrier component and side band components. The receiver of the interrogator is preferably configured to reduce the amplitude of the carrier component while maintaining the amplitudes of the side band components.
Variable phase shifters are disclosed to adjust the phase angle of the local continuous wave signal using a determined phase shift angle to reduce bleed through. The determined phase shift angle may be varied during operation of the interrogator. According to one aspect of the present invention, a phase shifter includes a power divider configured to provide plural quadrature components of an input signal, such as the local continuous wave signal. Plural mixers are provided to scale the quadrature components using the phase shift angle. A second power divider is provided to combine the scaled quadrature components to shift the phase angle of the input signal by the phase shift angle.
Methods of certain aspects of the present invention provide shifting of a phase angle of an input signal according to a phase shift angle. A method of one aspect includes providing the input signal into plural components. Thereafter, the components are scaled using the phase shift angle and combined to shift the phase angle of the input signal by the phase shift angle.